The quality or state of being devilish; wicked or mischievous nature.
From 'devilish' plus '-ness' (from Old English -nes/-ness, indicating abstract quality). The '-ness' suffix is extraordinarily productive in English for creating abstract nouns from adjectives.
The '-ness' suffix is English's favorite tool for creating abstract concepts—from 'good' we get 'goodness,' from 'sad' we get 'sadness.' It's so natural to English speakers that we barely notice it, but it's a recent innovation linguistically.
Complete word intelligence in one call. Free tier — 50 lookups/day.